1. Field of the Invention
The instant invention relates to improved ignition analyzers for multi-cylinder internal combustion engines and, in particular relates to improvements therein permitting the use of such analyzers with electronic ignition systems.
2. Description of the Prior Art
Ignition analyzers for use with multi-cylinder internal combustion engines are well known in the art. Conventional ignition analyzers may be considered to include a tachometer drive and display, a cathode ray oscilloscope drive and display and a power balance test circuit. The test circuit conventionally includes: (a) a counter for identifying the individual cylinder firings; (b) a switch for selecting a particular cylinder to be disabled and (c) a selectively operable shorting circuit controlled by the counter through the selector switch to disable the ignition system during the normal firing time of the cylinder selected. This power balance test circuit is normally utilized by selecting a particular cylinder and by observing the tachometer reading before and after disabling that cylinder so that the effect on engine performance of the normal operation of the cylinder selected, in terms of engine speed, may be determined.
These conventional analyzers require a first probe connected to a preselected cylinder, such as cylinder No. 1, for resetting the counter and second and third probes connected to the primary and secondary circuits of the ignition coil in order to display the signals developed therein and also to provide the count input for the counter. The shorting circuit is connected to the ungrounded side of the points. When the shorting circuit is actuated by the counter, the ungrounded side of the points is grounded by the shorting circuit so that the points effectively never open. The energy in the coil is therefore not discharged through the spark plug selected. The probe connected to the secondary circuit is normally a magnetic pickup positioned around the high tension lead between the primary side of the coil and the center of the distributor.
Such conventional analyzers cannot be used to analyze some of the recently developed electronic ignition systems such as the General Motors Corp., HEI, or high energy ignition system. In such systems the ignition coil is positioned within the distributor cap so that the secondary circuit is not readily accessible for signal detecting purposes and the points are replaced by a transistorized ignition circuit. Although a connection to the collector of this transistor is made accessible for connection to the engine tachometer, the remaining components are protected by covers. This prevents convenient access by the mechanic to connect probes associated with the analyzer. The power balance connection to the analyzer, which shorts the points to ground during the firing of the cylinder to be balanced, cannot be connected directly to the tachometer lead without harming the internal circuitry of the electronic ignition systems. Further details of the electronic ignition systems described above are not necessary for an understanding of the instant invention.